A. Field of Invention
The present invention relates to the field of magnetic recording, particularly to an improved suspension assembly for transducing heads.
B. Description of Prior Art
Currently, rigid-disk drive systems are widely utilized in the field of magnetic recording. A typical disk drive includes a stack of magnetic disks mounted on a rotating spindle. An electro-magnetic actuator controls an array of transducers which read and write binary digital information from and to the disks.
Each transducer (magnetic head) is mounted on an air-bearing slider loaded against the surface of a rotating disk by a spring suspension. The high-speed rotation of the magnetic disk generates a dynamic layer of air, thus allowing the slider to float in close proximity to the disk without physical contact with the disk surface. The separation between the slider and the magnetic disk during the operation of the drive is generally termed "flying height".
It is commonly known in the art that in order to elevate the density of magnetic recording and thereby to increase the storage capacity of the drive, it is necessary to reduce the separation between the magnetic head and the disk. Currently, the desired flying height is in the range of 0 to 75 nanometers (1 nm=10.sup.-9 m). However, as the flying height decreases, the possibility of contact between the rotating disk and the head also becomes more likely.
Since high-speed contact between the head and the disk, i.e., a head crash, permanently damages the transducer assembly as well as the magnetic disk, several magnetic-head suspension assemblies have been developed in order to eliminate this problem.
One such suspension assembly is manufactured by Hutchinson Technology, Inc., Hutchinson, Minn., and is designated as a Type 470. The suspension assembly, shown in FIG. 1, comprises a base mounting plate 10, a spring element 12, a load beam 14, and a flexure 16. Load beam 14 contains rails 18 and 20 and an apex 22. Flexure 16 has a load-bearing protuberance (or dimple) 24 and is connected to the load beam such that contact can be achieved between apex 22 and protuberance 24. A slider 26, which carries a transducing element (not shown), is rigidly attached to flexure 16.
The Type 470 suspension, however, has some notable shortcomings. Specifically, this assembly was intended for use at head-disk separations greater than 100 nm and thus cannot provide the magnetic recording density which could be obtained in the 0 to 75 nm range.
Several factors contribute to the inability of the Type 470 suspension to reliably achieve a flying height below 100 nm. Namely, these factors include a high head load; low lateral stiffness and high pitch and roll stiffnesses of the flexure; large slider footprint; relatively high vertical spring rate of the load beam; and low resonance frequency of the suspension assembly.
For illustration purposes, vertical bending of a load beam as well as lateral displacement, pitch, and roll of a flexure are shown in FIG. 2, where F.sub.vertical represents the vertical bending force acting on the load beam and F.sub.lateral, F.sub.pitch, and F.sub.roll represent forces causing lateral displacement, pitch, and roll of the flexure, respectively.
The Type 470 assembly requires a relatively high head load (preload of slider against the disk--otherwise known as gram load) of approximately 6 to 10 grams, contributing to increased stiction forces between the slider and the spinning disk. These forces may become large enough to stall the motor that rotates the hard-disk spindle and/or to bend the suspension assembly. Moreover, a high head load greatly increases the friction between the slider and the disk during start-up and shut-down of the disk drive, thus escalating the wear of disk-drive components.
Another shortcoming associated with high head load as well as with low lateral stiffness of flexure 16 is the so called "stick-slip" phenomenon of protuberance 24. In other words, acceleration of the suspension assembly by the actuator (not shown) induces lateral displacement of flexure 16 with respect to load beam 14. The misalignment between the load beam and the flexure causes head-positioning error. This flaw of the Type 470 suspension becomes especially salient in drives with high actuator acceleration.
Additionally, the Type 470 suspension has a slider which possesses comparatively large dimensions of 2.8 mm by 2.2 mm by 0.6 mm. Since the stiction forces between the slider and the disk are proportional to the footprint of the slider, a bigger slider produces greater stiction forces. Furthermore, the mass of a large slider lowers the resonance frequency of the suspension. Low-frequency resonances interfere with the performance of the servo-positioned electro-magnetic actuator of the drive, creating greater possibility of head-positioning error. Resonant vibration can also cause head crashes since, in combination with high pitch and roll stiffnesses of the Type 470 flexure, it impairs the ability of the slider to quickly respond to disk-curvature changes and disk asperities.
Also, high pitch and roll stiffnesses of the flexure contribute to poor magnetic performance of the transducer by adversely affecting the flying attitude of the slider. The transducing element is designed to perform optimally when the slider surface is parallel to the surface of the magnetic disk. Excessive stiffness of the flexure may cause the static orientation of the slider with respect to the disk to deviate from the normal position, thus inducing flying-height variations which interfere with the operation of the transducer.
Moreover, the load beam of the Type 470 suspension has inadequate rigidity which further contributes to resonance problems and impairs suspension integrity at high seek velocities. At the same time, the vertical spring rate of the load beam is relatively high, thus reducing the so called "Z-height" tolerance (Z-height is known in the art as the vertical distance from the mounting point of the base plate of the load beam to the surface of the magnetic disk). Therefore, imprecise mounting of the suspension assembly may lead to head crashes and accelerated wear of disk-drive components.
Furthermore, dampers (additional visco-elastic elements), which are often utilized to reduce vibration magnitude, are expensive and complicated. Dampers made of plastic are also responsible for such undesirable phenomena as outgassing and organic contamination of the disk drive.
In an attempt to eliminate some of the above-mentioned flaws, Hutchinson Technology, Inc., have produced a Type 16 suspension assembly, shown in FIG. 3. The spring element of the suspension has a window 28. The load beam possesses an integral flexure 30 which carries a reduced-footprint slider 32. The slider dimensions are 2 mm by 1.6 mm by 0.4 mm.
The Type 16 suspension has a low head load of 3.5 g, which in combination with the reduced-footprint slider allows to achieve head-disk separation in the range of 75 to 125 nm.
However, the Type 16 suspension cannot fly below 75 nm since its flexure is integral with the load beam and does not provide sufficient flexibility for the slider to flow over disk asperities at critically low altitudes. Hence, head crashes at head-disk separations below 75 nm present a serious problem. Also, high pitch and roll stiffnesses of the flexure contribute to poor magnetic performance of the transducer.
Moreover, even with window 28, the vertical spring rate of the load beam is high, reducing the Z-height tolerance when mounting the suspension assembly.
Additionally, the slider-bonding location of the Type 16 suspension is not well defined. For best performance, the center of mass of the slider should correspond with the geometrical center of the flexure. In the Type 470 suspension, the dimple marks the location of such a geometrical center, thus greatly simplifying accurate placement of the slider with respect to the flexure. However, since the flexure of the Type 16 suspension has no dimple, it is difficult to determine the precise slider-bonding location. If the center of mass of the slider is significantly shifted with respect to the geometrical center of the flexure, unacceptable flying-height fluctuation of the slider may result.
Furthermore, the Type 16 suspension does not have the same geometry as the Type 470, which is widely utilized in many types of disk drives. Therefore, the suspension-mounting systems of the disk drives must be redesigned in order to accommodate the Type 16 suspension, requiring a considerable investment of resources.